1. Technical Field
This invention relates to abrasive grinding wheels, and more particularly to disc grinding wheels having integrated mounting plates to facilitate mounting to face plates of surface grinding machines.
2. Background Information
Abrasive (i.e., grinding) wheels are widely used on conventional grinding machines and on hand-held angle grinders. When used on these machines the wheel is held by its center and is rotated at a relatively high speed while pressed against the work (i.e., workpiece). The abrasive surface of the grinding wheel wears down the surface of the work by the collective cutting action of abrasive grains of the grinding wheel.
Grinding wheels are used in both rough grinding and precision grinding operations. Rough grinding is used to accomplish rapid stock removal without particular concern for surface finish and burn. Examples of rough grinding include the rapid removal of impurities from billets, the preparing of weld seams and the cutting off of steel. Precision grinding is concerned with controlling the amount of stock removed to achieve desired dimensional tolerances and/or surface finish. Examples of precision grinding include the removal of precise amounts of material, sharpening, shaping, and general surface finishing operations such as polishing, and blending (i.e., smoothing out weld beads).
Conventional face grinding wheels or surface grinding wheels, in which the generally planar face of the grinding wheel is applied to the workpiece, may be used for both rough and precision grinding, using a conventional surface grinder or an angle grinder with the planar face oriented at an angle up to about 6 degrees relative to the workpiece. Conventional face grinding or surface grinding wheels are often fabricated by molding an abrasive particulate and bond mixture, with or without fiber reinforcements, to form a rigid, monolithic, bonded abrasive wheel. An example of suitable bonded abrasive includes alumina, silicon carbide and alumina zirconia grain in a resin bond matrix. Other examples of bonded abrasives include diamond, CBN, alumina, or silicon carbide grain, in a vitrified or metal bond. Various wheel shapes as designated by ANSI (American National Standards Institute) are commonly used in face or surface grinding operations. These wheel types include cylinder wheels (Type 2), abrasive discs (wheels having flat, annular grinding faces), straight cup wheels (Type 6), flaring cup (Type 11), dish wheels (Type 12), and depressed center wheels (Types 27 and 28).
Many of these conventional face grinding or surface grinding wheels/discs, such as the Type 6 straight cup wheels or others having a recessed center, may be conveniently mounted to a spindle/arbor of a grinding machine simply by use of a threaded fastener that passes through a center hole of the wheel and tightens the wheel against one or more spindle flanges. However, in many other applications, e.g., by virtue of their configuration and/or relatively large size, it is desirable to fasten these wheels at multiple locations disposed radially outward from their center holes in a manner that does not disrupt the continuity of the grinding face.
As shown in FIG. 1, this engagement is typically accomplished by embedding threaded metallic nuts 20 into the back face of an abrasive disc 30. The nuts are engaged by bolts 22 passing through a flange or face plate 24 of a grinding machine. This approach advantageously provides a relatively large number of distributed contact points, which securely fastens even relatively large wheels to the grinding machine (e.g., with up to 64 nut and bolt combinations 20, 22, for a wheel of 42 inches (107 cm) in diameter). A drawback to this approach, however, is that such wheels may require as many as 64 nuts each, placed in accordance with bolt hole patterns that may vary depending on the type and size of the wheel, and on the grinding machine manufacturer. As such, the manufacture of these discs, including the process steps associated with embedding the nuts in accordance with the desired hole patterns, tends to be relatively time consuming and labor intensive.
For example, the nuts 20 are typically embedded by means of complex fixturing used during mold filling and pressing operations. The fixturing is removed prior to thermal curing operations, and without the support provided by the fixturing, the nuts tend to move as the disc cures during firing, creating alignment problems when discs are mounted on grinding machines.
Alternatively, a fixture may be used to support the nuts during molding. The threaded engagement of the fixture and nuts enables the disc and plate to be fired as a unit. Once firing is complete, the fixture is removed, e.g., by unscrewing it, to release the fixture from the fired discs. Although firing the discs with the attached fixture tends to minimize any movement of the nuts, this method effectively prevents the fixture from being reused until firing is completed, which requires one to maintain a relatively large number of fixtures on hand. This requirement adds to the already large number of discrete parts required of a typical abrasive disc manufacturing operation, which may require thousands of parts to manufacture discs in a desired range of sizes and types.
Referring to FIG. 2, other mounting approaches use a steel mounting plate 36 having drilled and tapped mounting holes configured to receive a threaded stud or bolt passing through face plate 24 of the grinding machine. As shown, plate 36 is cemented to a rear face of the disc 30. Although this approach may operate satisfactorily for some (e.g., small diameter) abrasive wheels, the additional weight and cost associated with metallic plates 24 suitable for large wheels, e.g., up to 44 inches (112 cm) and 300 lbs (136 kg) would tend to be prohibitive.
Thus, a need exists for an improved surface grinding abrasive disc and method for fastening the disc to a grinding machine.